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71973 - Lycoming Two Bolt Flange Gasket

71973 - Lycoming Two Bolt Flange Gasket

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$ 2.20 $ 2.20

71973 – Lycoming™ Magneto Mounting Pad Gasket

Available now on the Airparts.aero Marketplace.

The Lycoming 71973 is a genuine OEM, flight-critical gasket designed to create a positive, leak-free seal between the magneto and the engine's accessory drive case. This precision-cut gasket is specified for the standard two-bolt magneto mounting flange found on the vast majority of Lycoming direct-drive engines. Its primary function is to contain the hot, pressurized engine oil that lubricates the magneto drive gear, preventing leaks that can create a fire hazard and compromise the cleanliness and safety of the engine compartment.

This component is manufactured from a specialized, high-performance gasket material, consisting of cellulose fibers fully impregnated with a fuel-and-oil-proof synthetic rubber binder. This composite construction ensures the gasket will not wick oil, shrink, or degrade from long-term exposure to the high temperatures and petroleum products inside the engine. It is a mandatory single-use part, essential for the proper installation of the engine's primary ignition system components.

Key Features

  • Genuine Lycoming OEM Part: Guarantees the precise die-cut dimensions and correct material composition required for a durable, leak-free seal.

  • Seals Pressurized Engine Oil: Engineered to reliably contain the hot lubricating oil present in the accessory gear case, preventing external leaks.

  • Protects Magneto Drive from Contaminants: Provides a barrier against the ingress of dirt, moisture, and other environmental contaminants into the engine.

  • Fuel/Oil-Resistant Fiber/Elastomer Composite: A specialized material that will not swell, harden, or break down when exposed to aviation fluids and high temperatures.

  • Single-Use Design for Maximum Seal Reliability: Engineered to be replaced every time the magneto is installed to ensure a fresh, perfectly conforming sealing surface.

Technical Specifications

  • Part Number: 71973

  • Component Type: Magneto Mounting Gasket

  • OEM Manufacturer: Lycoming Engines

  • Material: Cellulose Fiber with a high-percentage, fuel/oil-resistant Synthetic Rubber (Nitrile) Binder.

  • Application: Seals the standard two-bolt mounting flange of Bendix or Slick magnetos to the accessory case.

Engine Compatibility

The 71973 gasket is one of the most widely used parts in the Lycoming ecosystem and is specified for nearly all direct-drive Lycoming engine families, including but not limited to:

  • O-235, O-320, IO-320, AEIO-320 Series

  • O-360, IO-360, AEIO-360, TIO-360 Series

  • O-540, IO-540, AEIO-540, TIO-540, LTIO-540 Series

  • IO-580 Series

  • IO-720 Series

Crucial Note: The specific engine model and serial number must be checked against the latest revision of the official Lycoming Parts Catalog to ensure correct part number applicability. The engine parts catalog is the final authority.

Fits the following Engine models:
Lycoming™

  1. O-235   (C1, C1A, C1B, C1C, C2A, C2B, C2C, E1, E2A, E2B, F1, F1B, F2A, F2B, G1, G1B, G2A, G2B, H2C, J2A, J2B, K2A, K2B, K2C, L2A, L2C, M1, M2, M2C, M3C, N2A, N2C, P1, P2A, P2C, P3C)
  2. O-290   (11, D, D2, D2A, D2B, D2C)
  3. O-320   (no suffix, A1A, A2B, A2A, A2B, A2C, A2D, A3A, A3B, A3C, B1A, B1B, B2A, B2B, B2C, B2D, B2E, B3A, B3B, B3C, C1A, C1B, C2A, C2B, C2C, C3A, C3B, C3C, D1A, D1B, D1C, D1D, DIF, D2A, D2B, D2C, D2F, D2G, D2H, D2J, D3G, E1A, E1B, E1C, EIF, E1J, E2A, E2B, E2C, E2D, E2E, E2F, E2G, E2H, E3D, E3H, HIAD, HIBD, H2AD, H2BD, H3AD, H3BD)
  4. IO-320   (A1A, A2A, B1A, B1B, B1C, B1D, B2A, C1A, D1A, D1B, E1A, E1B, E2A, E2B, F1A)
  5. AIO-320   (A1A, A1B, A2A, A2B, B1B, C1B)
  6. LIO-320   (B1A, C1A)
  7. AEIO-320   (D1B, D2B, E1A, E1B, E2A, E2B)
  8. O-340   (A1A, A2A, B1A)
  9. O-360   (A1A, A1AD, A1C, A1D, A1F, A1F6, A1G, A1G6, A1G6D, A1H, A1H6, A1LD, A1P, A2A, A2D, A2E, A2F, A2G, A2H, A3A, A3AD, A3D, A4A, A4AD, A4D, A4G, A4J, A4K, A4M, A4N, A4P, A5AD, B1A, B1B, B2A, B2B, B2C, C1A, C1C, C1E, C1F, C1G, C2A, C2B, C2C, C2D, C2E, C4F, C4P, D1A, D2A, D2B, E1A6D, F1A6, G1A6, J2A)
  10. H0-360   (A1A, B1A, B1B, C1A)
  11. IO-360   (A1A, A1B, A1B6, A1B6D, A1C, A1D, A1D6, A1D6D, A2A, A2B, A2C, A3B6, A3B6D, B1A, B1B, B1C, B1D, B1E, B1F, B1F6, B1G6, B2E, B2F, B2F6, B4A, C1A, C1B, C1C, C1C6, C1D6, C1E6, C1F, C1G6, D1A, E1A, F1A, J1AD, J1A6D, K2A, L2A, M1A, M1B)
  12. LO-360   (A1G6D, A1H6, E1A6D)
  13. TO-360   (A1A6D, C1A6D, E1A6D, F1A6D)
  14. VO-360   (A1A, A1B, B1A)
  15. AIO-360   (A1A, A1B, A2A, A2B, B1B)
  16. HIO-360   (A1A, A1B, B1A, B1B, C1A, C1B, D1A, E1AD, E1BD, F1AD)
  17. IVO-360-A1A
  18. LIO-360-C1E6
  19. TIO-360   (A1A, A1B, A3B6, C1A6D, C1F)
  20. AEIO-360   (A1A, A1B, A1B6, A1C, A1D, A1E, A1E6, A2A, A2B, A2C, A3B6D, B1B, B1D, B1F, B1F6, B1G6, B1H, B2F, B2F6, B4A, H1A, H1B) 
  21. LHIO-360   (C1A, C1B, F1AD)
  22. O-435   (25, A)
  23. GO-435   (11, 11A, 11B, C1B1, C2, C2A, C2A2, C2B, C2B1, C2B2, C2B2-6, C2E)
  24. VO-435   (A1A, A1B, A1C, A1D, A1E, A1F, B1A)
  25. GSO-435   (B, B2)
  26. TVO-435   (A1A, B1A, B1B, C1A, D1A, D1B, E1A, F1A, G1A, G1B)
  27. O-480   (1, 3)
  28. GO-480   (A1A, B, B1, B1A6, B1B, B1C, B1D, C1B6, C1D6, C2C6, C2D6, C2E6, D1A, F1A6, F2A6, F2D6, F3A6, F3B6, F4A6, F4B6, F6, G1A6, G1B6, G1D6, G1H6, G1J6, G2D6, G2F6)
  29. GSO-480   (A1A, A1A6, A2A6, B1A6, B1B3, B1B6, B1C6, B1E6, B1F6, B1G6, B1J6, B2C6, B2D6, B2G6, B2H6)
  30. IGO-480   (A1A6, A1B6)
  31. IGSO-480   (A1A6, A1B6, A1C6, A1D6, A1E6, A1F3, A1F6, A1G6)
  32. O-540-9   (9A, A1A, A1A5, A1B5, A1C5, A1D, A1D5, A2B, A3D5, A4D5, B1A5, B1B5, B1D5, B2A5, B2B5, B2C5, B4A5, B4B5, D1A5, E4A5, E4B5, E4C5, F1A5, F1B5, G1A5, G2A5, H1A5, H1A5D, H1B5, H1B5D, H2A5, H2A5D, H2B5D, J1A5D, J1B5D, J1C5D, J1D5D, J2A5D, J2B5D, J2C5D, J2D5D, J3A5, J3A5D, J3C5D, L3C5D)
  33. IO-540   (A1A5, B1A5, B1B5, B1C5, C1B5, C1C5, C2C, C4B5, C4B5D, C4C5, C4D5, C4D5D, D4A5, D4B5, D4C5, E1A5, E1B5, E1C5, G1A5, G1B5, G1C5, G1D5, G1E5, G1F5, J4A5, K1A5, K1A5D, K1B5D, K1C5, K1D5, K1E5, K1E5D, K1F5, K1F5D, K1H5, K1J5, K1J5D, K1K5, K2A5, L1A5, L1A5D, L1B5D, L1C5, M1A5, M1A5D, M1B5, M1B5D, M1C5, M2A5D, N1A5, N1A5D, P1A5, R1A5, S1A5, T4A5D, T4B5, T4B5D, T4C5D, U1A5D, U1B5D, V4A5, V4A5D, W1A5, W1A5D, W3A5D, AA1A5, AA1B5, AB1A5, AC1A5, AE1A5)
  34. VO-540   (A1A, A2A, B1A, B1B, B1B3, B1C, B1D, B1E, B1F, B1H3, B2A, B2C, B2D, B2E, B2G, C1A, C1B, C1C3, C2A, C2B, C2C)
  35. HIO-540-A1A
  36. IGO-540   (A1A, A1B, A1C, B1A, B1B, B1C)
  37. IVO-540-A1A
  38. TIO-540   (A1A, A1B, A1C, A2A, A2B, A2C, C1A, E1AD, G1A, H1A, J2B, J2BD, K1AD, N2BD, R2AD, S1AD, T2AD, U2A, V2AD, W2A, AA1AD, AB1D, AB1BD, AE2A, AF1A, AF1B, AG1A, AH1A, AJ1A, AK1A)
  39. TVO-540-A1A
  40. AEIO-540   (D4A5, D4B5, D4C5, D4D5, L1B5, L1D5)
  41. IGSO-540   (A1A, A1C, A1D, A1E, A1F, A1H, B1A, B1C)
  42. LTIO-540   (F2BD, J2B, J2BD, K1AD, N2BD, R2AD, U2A, V2AD, W2A
  43. TIVO-540-A2A
  44. TIO-541   (A1A, E1A4, E1B4, E1C4, E1D4)
  45. TIGO-541   (D1A, D1B, E1A, G1AD)
  46. IO-720    (A1A, A1B, A1BD, B1B, B1BD, C1B, C1BD, D1B, D1BD, D1C, D1CD)

Applications

This gasket is a mandatory replacement part during any maintenance that requires the removal or installation of a magneto.

  • Complete Engine Overhaul

  • 500-Hour Magneto Inspection and Repair

  • Magneto Replacement or Timing Adjustments

Why Choose 71973?

Choosing a genuine Lycoming 71973 is a critical decision for preventing persistent and dangerous engine oil leaks. The accessory case is a difficult area to work in, and a leaking magneto gasket can spray oil over hot exhaust components, creating a significant fire risk. Using a non-certified gasket made from an inferior material can lead to rapid degradation, wicking, or loss of clamping force, resulting in a guaranteed leak. The genuine Lycoming part is precision-cut from the correct, certified composite material, ensuring a reliable, long-lasting seal that protects your engine and maintains a safe, clean firewall-forward environment.

The 71973 is not a simple paper gasket; it is an engineered composite material designed for optimal flange sealing. The material utilizes a non-asbestos, cellulose fiber matrix that provides the gasket's core structural stability and resistance to extrusion under the clamping pressure of the mounting nuts. This fibrous matrix is then saturated and bonded under heat and pressure with a high-percentage Nitrile (NBR) elastomer. The Nitrile binder provides three critical properties that the fiber alone cannot: 1) Impermeability: It fills the microscopic voids within the fiber matrix, rendering the gasket impervious to the pressurized, low-viscosity engine oil. 2) Conformability: The rubber allows the gasket to flow and conform to any minor surface irregularities on the machined aluminum flanges of the magneto and accessory case, ensuring a complete seal. 3) Resilience: The elastomer gives the gasket the ability to maintain a constant sealing pressure (stress retention) even as the joint experiences minor movements due to the engine's vibration and thermal expansion cycles. This composite approach provides a vastly superior and more durable seal compared to a simple fiber or simple elastomer gasket alone.

Note: This is a single-use component. This gasket MUST be replaced with a new one every time a magneto is installed or reinstalled. Re-using a compressed gasket will result in an oil leak. The magneto and engine mounting surfaces must be perfectly clean, dry, and free of any old gasket material or sealant prior to installation. The magneto mounting nuts should be torqued evenly to the value specified in the engine maintenance manual.

Documentation

The definitive part number applicability and installation procedures are detailed in the applicable Lycoming engine maintenance, overhaul, and parts catalogs for the specific engine model.